We will use probes (filipin and polymyxin-B) that localize specific membrane lipids (Beta-hydroxysterols and anionic phospholipids) in conventional transmission and freeze fracture electron micrographs to quantitate their distribution in specific membrane domains of intestinal epithelial cells in normal rat and human small intestine, intestinal disease (celiac sprue), during absorption of dietary fat, during intestinal maturation and during experimentally increased and decreased intestinal cholesterol synthesis. Since membrane lipid content and distribution profoundly influence membrane function, such studies should enhance our understanding of intestinal absorptive and digestive processes in health and disease. We will also study by these techniques the structure of isolated intestinal microvillus and basolateral membranes to determine if the structure of these widely used membrane preparations is comparable to that observed in intact mucosa. We will determine how microvillus membrane structure and chemical composition are altered following exposure to physiological lipid dispersions. This system should provide information on the membrane changes seen during the initial phase of fat absorption, the transport of lipid across the microvillus membrane. To examine host factors influencing the distinctive adherence to and penetration of the follicular epithelium overlying Peyer's patches by type 1 and type 3 mammalian reoviruses, we will determine at the ultrastructural level lectin binding characteristics of and, by immunocytochemical methods, the histocompatibility antigen distribution on the apical surface of follicular M cells and absorptive cells. Characterization of factors influencing penetration of the intestinal barrier by microorganisms is of fundamental importance to our understanding of the mechanisms by which microorganisms breach the intestinal mucosal barrier to invade the host. We will also use type 1 reovirus which binds selectively to the apical surface of M cells as a specific probe to study M cell morphogenesis and derivation in neonatal and adult rodent ileum. We will determine at the ultrastructural level the lectin binding characteristics of the apical surface of small intestinal epithelial cells in fetal and neonatal rats to correlate the appearance of cell specific surface glycoconjugates with intracellular cytodifferentiation.